There has been known a subjective optometry apparatus that measures optical characteristics (refractive power or the like) of an examinee's eye by disposing an optical elements such as a spherical lens or a cylindrical lens in front of the examinee's eye and presenting an examination target to the examinee's eye via the optical elements (for example, see JP-A-H05-176893). When the optical characteristics of the examinee's eye are measured, the position adjustment (alignment) of the examinee's eye and the subjective optometry apparatus is performed.
In a subjective examination, a different examination target depending on a visual acuity value of an examinee's eye is presented to the examinee's eye such that every examination target has a constant size, by the position adjustment (alignment) of the examinee's eye and the subjective optometry apparatus. For example, the inventors study a subjective optometry apparatus, as an example, which includes a light projecting optical system that projects a target light flux to an examinee's eye and a fixed optical element that guides the target light flux from the light projecting optical system to the examinee's eye so as to have an optically predetermined examination length, performs the position adjustment with respect to the examinee's eye by moving a measurement unit accommodating the light projecting optical system, and projects, via the fixed optical element to the examinee's eye, the target light flux from the light projecting optical system of the position-adjusted measurement unit.
Incidentally, in such a subjective optometry apparatus, especially, in a subjective optometry apparatus in which a target light flux is projected toward an examinee's eye via a fixedly disposed optical element, a change in position of the target light flux incident to the optical element is found due to a state of alignment in some cases. When an incident position of the target light flux changes with respect to the optical element, an image location of the target light flux moves, and thus a projection magnification of the examination target presented to the examinee's eye changes. Therefore, even when the examinee's eye and the subjective optometry apparatus are appropriately aligned, it may not be possible to measure optical characteristics of the examinee's eye.